(1) Field of the Invention
The present invention relates to methods for producing protein and glycoproteins in Pichia pastoris that lack detectable cross binding activity to antibodies made against host cell antigens. In particular, the present invention relates to using recombinant Pichia pastoris strains that do not display a β-mannosyltransferase 2 activity with respect to an N-glycan or O-glycan and do not display at least one activity selected from the group consisting of β-mannosyltransferase 1, 3, and 4 activity with respect to an N-glycan or O-glycan. These recombinant Pichia pastoris strains can produce proteins and glycoproteins that lack detectable α-mannosidase resistant β-mannose residues thereon. The present invention further relates to methods for producing bi-sialylated human erythropoietin in Pichia pastoris that lack detectable cross binding activity to antibodies against host cell antigens.
(2) Description of Related Art
The ability to produce recombinant human proteins has led to major advances in human health care and remains an active area of drug discovery. Many therapeutic proteins require the posttranslational addition of glycans to specific asparagine residues (N-glycosylation) of the protein to ensure proper structure-function activity and subsequent stability in human scrum. For therapeutic use in humans, glycoproteins require human-like N-glycosylation. Mammalian cell lines (e.g., CHO cells, human retinal cells) that can mimic human-like glycoprotein processing have several drawbacks including low protein titers, long fermentation times, heterogeneous products, and continued viral containment. It is therefore desirable to use an expression system that not only produces high protein titers with short fermentation times, but can also produce human-like glycoproteins.
Fungal hosts such as the methylotrophic yeast Pichia pastoris have distinct advantages for therapeutic protein expression, for example, they do not secrete high amounts of endogenous proteins, strong inducible promoters for producing heterologous proteins are available, they can be grown in defined chemical media and without the use of animal sera, and they can produce high titers of recombinant proteins (Cregg et al., FEMS Microbiol. Rev. 24: 45-66 (2000)). However, glycosylated proteins expressed in P. pastoris generally contain additional mannose sugars resulting in “high mannose” glycans, as well as mannosylphosphate groups which impart a negative charge onto glycoproteins. Glycoproteins with either high mannose glycans or charged mannans present the risk of eliciting an unwanted immune response in humans (Takeuchi, Trends in Glycosci. Glycotechnol. 9:S29-S35 (1997); Rosenfeld and Ballou, J. Biol. Chem. 249: 2319-2321 (1974)). Accordingly, it is desirable to produce therapeutic glycoproteins in fungal host cells wherein the pattern of glycosylation on the glycoprotein is identical to or similar to that which occurs on glycoproteins produced in humans and which do not have detectable β-mannosylation.
As evidenced by the presence of protective antibodies in uninfected individuals, β-linked mannans are likely to be immunogenic or adversely affect the individual administered a therapeutic protein or glycoprotein comprising β-linked mannans. Additionally, exposed mannose groups on therapeutic proteins are rapidly cleared by mannose receptors on macrophage cells, resulting in low drug efficacy. Thus, the presence of β-linked mannose residues on N- or O-linked glycans of heterologous therapeutic proteins expressed in a fungal host, for example, P. pastoris, is not desirable given their immunogenic potential and their ability to bind to clearance factors.
Glycoproteins made in P. pastoris have been reported to contain β-linked mannose residues. In 2003, Trimble et al. (Glycobiol. 14: 265-274, Epub December 23) reported the presence of β-1,2-linked mannose residues in the recombinant human bile salt-stimulated lipase (hBSSL) expressed in P. pastoris. The genes encoding several β-mannosyltransferases have been identified in Pichia pastoris and Candida albicans (See U.S. Pat. No. 7,465,577 and Mille et al., J. Biol. Chem. 283: 9724-9736 (2008)).
In light of the above, there is a need to provide methods for making recombinant therapeutic proteins or glycoproteins in methylotrophic yeast such as Pichia pastoris that lack eptitopes that might elicit an adverse reaction in an individual administered the recombinant therapeutic protein or glycoprotein. A method for determining whether a recombinant therapeutic protein or glycoprotein provides a risk of eliciting an adverse reaction when administered to an individual is to contact the recombinant therapeutic protein or glycoprotein to an antibody prepared against total host cell antigens. This is of particular concern for proteins or glycoproteins intended for chronic administration. The lack of cross binding to the antibody indicates that the recombinant therapeutic protein or glycoprotein lacks detectable cross binding activity to the antibody and is unlikely to elicit an adverse reaction when administered to an individual. Thus, there is a need for methods for producing a recombinant therapeutic protein or glycoprotein that lacks detectable cross binding activity to the antibody and is unlikely to elicit an adverse reaction when administered to an individual.